Electrochromic devices produced by depositing a composition containing a crosslinkable polymer onto a suitable support (for example one of the electrodes), followed by in situ crosslinking, are known. EP-0 850 920 describes the production of an electrochromic device via a process that consists in applying a polymerizable composition onto a glass plate coated with a layer of WO3 and a tin oxide conductive sublayer, in photopolymerizing by UV irradiation to obtain a membrane that is optically transparent in the visible range and adherent to the support, and then in assembling this membrane with a counterelectrode formed from a glass plate bearing a layer of hydrogenated iridium oxide HxIrO2 and a tin oxide sublayer. In this process, the polymerizable composition is formed from the lithium salt of trifluoromethanesulfonyl(1-acryloyl-2,2,2-tri-fluoroethanesulfonyl)imide, poly(ethylene glycol)dimethacrylate, silica particles and xanthone. However, xanthone has coloring properties, and its presence in the electrolyte reduces the transparency. In addition, silica dissolves very poorly in a polymer without solvent, it increases the porosity of the material and it also contributes toward reducing the transparency.
WO 97/26661 describes an electrochromic device comprising an assembly that is formed by two electrochromic layers separated by a film of ion-conducting material and which is placed between two convex lenses. Each electrochromic layer is borne by a substrate coated with a conductive oxide of the ITO type. The ion-conducting material forms an ion-conducting polymer electrolyte and it is formed by a proton-conducting polymer, for example a 2-acrylamido-2-methylpropanesulfonic acid homopolymer. The polymer film is produced by depositing onto one of the electrodes a liquid reaction mixture containing the polymer precursor dissolved in a liquid solvent, for example a mixture of water and NMP. The presence of the liquid solvent in the composition intended to form the solid electrolyte necessitates removal of the liquid solvent, the result of which is that the film of polymer electrolyte resulting therefrom is porous. However, the porosity of a layer of an electrochromic device harms the optical quality of the electrochromic device.